why does the boiling point from NaCl to NaBr to NaI increase when molecular weight increases?

Answer 1

iodine has more electrons than bromine, and bromine has more electrons than chlorine. more electrons result in a stronger van der Waal's interaction to the cation. you'd think sodium iodide has the highest boiling point and melting point among these three compounds.

however, chloride is smaller than bromide, bromide is smaller than iodide. because they all have the same charge, the lattice energy is largest in sodium chloride, and smallest in sodium iodide.

E = (cation charge)(anion charge) / (distance between them)

this is an opposite trend to van der Waal's interaction. the shorter distance between the nuclei of cation and chloride in lattice energy is a more important factor than van der Waal's interaction.

so, NaCl has the highest boiling point and melting point among these three.

Answer 2

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RE:
why does the boiling point from NaCl to NaBr to NaI increase when molecular weight increases?

Answer 3

Boiling Point Of Nabr

Answer 4

are you sure it is boiling point? it could be melting point. Because greater formula weights require greater energy to disrupt ionic bonds so that a higher melting tempratureis required to melt substances in increasing molecular/formula weights.

Answer 5

The molecular bonds are more powerful and need much more energy to break.